Electric storage device and electric storage apparatus

ABSTRACT

An electric storage device includes: an electrode assembly in which electrodes are wound such that paired curved portions and a straight portion connecting the paired curved portions are formed; a case which houses the electrode assembly, the case comprising a convex part protruding toward the straight portion of the electrode assembly to support the straight portion; and a support portion which supports the curved portion toward an inside of the electrode assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese patent applications No.2013-206086, filed on Oct. 1, 2013, and No. 2014-173813, filed on Aug.28, 2014, which are incorporated by reference.

FIELD

The present invention relates to an electric storage device which can becharged and discharged.

BACKGROUND

Conventionally, there is a known electric storage device such as asecondary battery which can be charged and discharged. The electricstorage device includes an electrode assembly formed by layeringpositive electrodes and negative electrodes with separators interposedtherebetween and a case housing the electrode assembly. Among electricstorage devices of this type, as shown in FIG. 8, there is one in whicha case 101 has a substantially rectangular parallelepiped external shapecapable of housing an electrode assembly 102 inside itself and pairedside walls 101 a, 101 a forming the case 101 have a plurality of convexparts 104, 104, . . . protruding toward an inside of the case 101(JP-A-62-126566).

In such an electric storage device 100, the convex parts 104 presssubstantially the entire electrode assembly 102 toward an inner side ina layered direction at predetermined pressure to narrow intervalsbetween the adjacent electrodes 103 in substantially the entireelectrode assembly 102. As a result, charge-discharge efficiency of theelectric storage device 100 is enhanced.

SUMMARY

The following presents a simplified summary of the invention disclosedherein in order to provide a basic understanding of some aspects of theinvention. This summary is not an extensive overview of the invention.It is intended to neither identify key or critical elements of theinvention nor delineate the scope of the invention. Its sole purpose isto present some concepts of the invention in a simplified form as aprelude to the more detailed description that is presented later.

An object of the present invention to provide an electric storage deviceincluding an electrode assembly which is formed by winding electrodesand in which partial clearances are less liable to be formed between theadjacent electrodes.

An electric storage device according to an aspect of the inventionincludes: an electrode assembly in which electrodes are wound such thatpaired curved portions and a straight portion connecting the pairedcurved portions are formed; a case which houses the electrode assembly,the case comprising a convex part protruding toward the straight portionof the electrode assembly to support the straight portion; and a supportportion which supports the curved portion toward an inside of theelectrode assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present invention will becomeapparent from the following description and drawings of an illustrativeembodiment of the invention in which:

FIG. 1 is a perspective view of a non-aqueous electrolyte secondarybattery according to a present embodiment;

FIG. 2 is a sectional view along a line II-II in FIG. 1;

FIG. 3 is an enlarged sectional view along a line III-III in FIG. 1;

FIG. 4 is a schematic block diagram explaining a structure in whichsupport portions are formed by using parts of an insulating member;

FIG. 5 is a schematic block diagram explaining an arrangement of supportportions in a case housing two electrode assemblies;

FIG. 6 is a drawing explaining convex parts of a case according toanother embodiment;

FIG. 7 is a drawing explaining convex parts of a case according toanother embodiment;

FIG. 8 is a partial cutaway perspective view of a prior-art electricstorage device;

FIG. 9 is a vertical sectional view of an electric storage deviceaccording to a comparative example; and

FIG. 10 is a perspective view of an electric storage apparatus.

DESCRIPTION OF EMBODIMENTS

An electric storage device 200 shown in FIG. 9 includes an electrodeassembly 202 formed by winding band-shaped electrodes 201, the electrodeassembly 202 being housed in a case 203. The band-shaped electrodes 201are wound such that a section orthogonal to a winding axis has anelliptic shape. The case 203 has paired side walls 205, 205 which areparallel to a major axis direction (a vertical direction in FIG. 9) ofthe electrode assembly 202 and which respectively have convex parts 204protruding toward the electrode assembly 202. The convex parts 204 pinchthe electrode assembly 202 in a minor axis direction (a left-rightdirection in FIG. 9) so as to narrow intervals between the adjacentelectrodes 201 in the wound electrode assembly 202.

In this electric storage device 200, if expansion and contraction of theelectrode assembly 202 is repeated due to repetition of charge-dischargeor the like, displacements of the electrodes 201 gather in curvedportions (which are end portions of the electrode assembly 202 in themajor axis direction and also are curved portions of the electrodes 201)202A not pressed by the convex parts 204. Then, partial clearances andthe like are formed between the electrodes 201 layered in the curvedportions 202A. If the partial clearances are formed between theelectrodes 201 forming the electrode assembly 202 in this manner,charge-discharge efficiency is reduced.

An electric storage device according to an aspect of the inventionincludes: an electrode assembly in which electrodes are wound such thatpaired curved portions and a straight portion connecting the pairedcurved portions are formed; a case which houses the electrode assembly,the case comprising a convex part protruding toward the straight portionof the electrode assembly to support the straight portion; and a supportportion which supports the curved portion toward an inside of theelectrode assembly.

With this structure, in the case, the straight portion is supported bythe convex part and also the curved portion is supported by the supportportion toward the inside of the electrode assembly. Therefore, it ispossible to suppress gathering of displacement of the electrodes in thecurved portion, the gathering caused by repetition of expansion andcontraction of the electrode assembly during charge-discharge, or thelike. In this way, it is possible to prevent forming of partialclearances between the electrodes layered at the curved portions of theelectrode assembly. Here, the curved portions of the electrode assemblyrefer to portions of which peripheral faces are curved, and the straightportion of the electrode assembly refers to a portion of whichperipheral face is substantially straight.

The support portion may support at least one of the paired curvedportions of the electrode assembly.

With this structure, it is possible to prevent forming of the partialclearances between the electrodes layered at least at one of the pairedcurved portions. In this way, as compared with a structure in which onlya straight portion of an electrode assembly is supported, the intervalsbetween the electrodes forming the electrode assembly become narrow,which increases charge-discharge efficiency.

The case may have a substantially rectangular frame-shaped section andhouse the electrode assembly such that a side of the substantiallyrectangular frame-shaped section extends along the straight portion, thesupport portion may be disposed in a corner portion of the substantiallyrectangular frame-shaped section in the case.

In this manner, because the support portion is disposed in the cornerportion of the substantially rectangular frame-shaped section in thecase, the support portion is supported by the case from two directions.In this way, the support portion can effectively support the curvedportion of the electrode assembly toward inside. As a result, it ispossible to more reliably prevent forming of the partial clearancesbetween the electrodes layered in the curved portion.

The support portion may be disposed while being elastically deformedbetween the case and the curved portion of the electrode assembly.

In this manner, the curved portion of the electrode assembly issupported by utilizing resilience generated by the elastic deformationof the support portion. Therefore, even if the electrode assemblyexpands and contracts due to the charge-discharge or the like, i.e.,changes in size (winding diameter), the support portion can follow thechange in size and continue to support the curved portion.

The electric storage device may include an insulating member disposedbetween the case and the electrode assembly to insulate the case and theelectrode assembly from each other, wherein the support portion may be apart of the insulating member.

With this structure, the support portion is formed by using the part ofthe insulating member for insulating the case and the electrode assemblyfrom each other, and therefore it is possible to reduce the number ofparts forming the electric storage device as compared with a case inwhich a member forming the support portion is disposed separately.

The insulating member may have a portion curved to bulge toward theelectrode assembly, and the curved portion of the insulating member maysupport the curved portion of the electrode assembly.

In this manner, with the simple structure in which the part of theinsulating member is curved to bulge toward the electrode assembly, itis possible to form the support portion for supporting the curvedportion toward the inside of the electrode assembly.

A dimension of the support portion in a direction orthogonal to awinding direction of the electrodes is preferably substantially equal toor greater than a dimension of the electrode assembly in the directionorthogonal to the winding direction.

With this structure, substantially the entire curved portion in thedirection orthogonal to the winding direction of the electrodes issupported at the curved portion, and therefore it is possible toeffectively prevent forming of the partial clearances between thelayered electrodes at substantially the entire curved portion in thedirection orthogonal to the winding direction.

Preferably, the case may have a plurality of the convex parts.

With this structure, because the straight portion of the straightportion is supported by plural convex parts, it is possible toeffectively prevent forming of the partial clearances between thelayered electrodes at the straight portion due to the charge-discharge.

The case may have a wall portion having a wave-shaped inner surface anda wave-shaped outer surface and having a substantially constantthickness, and the wave-shaped inner surface forms a plurality of theconvex parts, and the plurality of convex parts support the straightportion of the electrode assembly at intervals.

With this structure, the straight portion of the electrode assembly issupported by the plurality of convex parts, and therefore it is possibleto more effectively suppress forming of the clearances between theelectrodes in the straight portion due to the charge-discharge.Furthermore, by providing the plurality of convex parts, rigidity of thecase increases.

In the above-described structure, preferably, the case has asubstantially-rectangular bottom wall portion when viewed in a directionof a normal, the wall portion has paired wall portions extendingsubstantially vertically from paired long sides of the bottom wallportion, and a maximum clearance between the paired wall portions isgreater than a dimension in a short-side direction of the bottom wallportion.

With this structure, when the plurality of electric storage devices arearranged with the straight portions being opposed and bound by arestraining member, the convex parts are pressed by the adjacent batteryor the restraining member, and therefore the convex parts can reliablysupport the straight portion.

According to another aspect of the invention, there is provided anelectric storage apparatus including the electric storage device and arestraining member.

According to the aspects of the invention, it is possible to provide theelectric storage device including the electrode assembly which is formedby winding the electrodes and in which partial clearances are lessliable to be formed between the adjacent electrodes, and the electricstorage apparatus including the electric storage device.

An embodiment of the invention will be described below with reference toFIGS. 1 to 3. An electric storage device according to the embodiment isa nonaqueous electrolyte secondary battery (hereafter, merely referredto as “battery”) such as a lithium ion secondary battery.

As shown in FIGS. 1 to 3, a battery 10 includes a case 20, an electrodeassembly 12, paired current collectors 14, 14, an insulating member 30,support members (support portions) 32, and paired terminal portions 16,16. In the battery 10, the winding-type electrode assembly 12 is housedin the case 20, a section of the electrode assembly 12 orthogonal to awinding axis having an elliptic shape.

The case 20 includes a case main body 22 and a lid body 24. The case 20houses, in an inner space S surrounded with the case main body 22 andthe lid body 24, the electrode assembly 12, the paired currentcollectors 14, 14, electrolyte solution, and the like. The case mainbody 22 and the lid body 24 are made of aluminum or aluminum-based metalmaterial such as an aluminum alloy, for example. By welding end portionsof the case main body 22 and the lid body 24 to each other, the case 20is formed.

The case main body 22 has a flat rectangular cylindrical shape having abottom. Specifically, the case main body 22 has a bottom wall portion220 and a rectangular cylindrical peripheral wall 221 rising from aperipheral edge of the bottom wall portion 220 in a direction of anormal to the bottom wall portion 220. The bottom wall portion 220 is ina rectangular shape long in one direction and having four arc-shapedcorners when viewed in the direction of the normal to the bottom wallportion 220. The peripheral wall 221 has paired long wall portions 222,222 rising from long side positions of the peripheral edge of the bottomwall portion 220 and paired short wall portions 223, 223 rising fromshort-side positions of the peripheral edge of the bottom wall portion220. In the following description, a long-side direction of the bottomwall portion 220 will be referred to as an X-axis direction, ashort-side direction of the bottom wall portion 220 will be referred toas a Y-axis direction, and the direction of the normal to the bottomwall portion 220 will be referred to as a Z-axis direction (see FIG. 1).

Each of the long wall portions 222 has the plurality of convex parts225, 225, . . . protruding toward an inner side of the case 20. To putit concretely, the long wall portion 222 has a triangular wave-shapedportion 222A which repeatedly bends alternately toward an inside and anoutside of the case 20 at a position corresponding to a straight portion12B of the electrode assembly 12 in a section along the Y-Z plane. Atthe triangular wave-shaped portion 222A, angle portions protruding fromportions 224 positioned on an outermost side of the case 20 toward theinner side (toward the electrode assembly) form the convex parts 225.

As shown in FIG. 3, in the embodiment, the portions 224 of thetriangular wave-shaped portions 222A positioned on the outermost sidesof the case 20 are positioned on outer sides in the Y-axis directionthan end portions in the Y-axis direction of the bottom wall portion220. In other words, a longest interval between the paired long wallportions 222 is longer than a dimension in a short-side direction of thebottom wall portion 220. Therefore, if a plurality of batteries arearranged with the long wall portions 222 being opposed and bound by arestraining member (if the plurality of batteries are pressed in adirection orthogonal to the long wall portions 222 (see FIG. 10)), theportions 224 are pressed by the adjacent batteries or the restrainingmember and, as a result, the convex parts 225 reliably support (orpress) the straight portion 12B of the electrode assembly 12.

In the embodiment, dimensions in the Z-axis direction of the triangularwave-shaped portions 222A are substantially equal to a dimension in theZ-axis direction of the straight portion of the electrode assembly 12.

In the paired long wall portions 222, 222 arranged parallel to eachother, the respective convex parts 225 are arranged to protrude in adirection approaching each other at opposed positions in the Z-axisdirection. In this way, the respective convex parts 225 protrude towardthe straight portion 12B of the electrode assembly 12 to support thestraight portion 12B inward in a minor axis direction of the electrodeassembly 12. In other words, the opposing paired convex parts 225, 225make up a set, the plurality of sets of convex parts 225 are arranged inthe Z-axis direction, and each of the sets pinches the straight portion12B (electrode assembly 12) in the minor axis direction of the electrodeassembly 12.

In the specification, the sentence, “the convex parts 225 support thestraight portion 12B of the electrode assembly 12” includes a case inwhich the convex parts 225 are directly or indirectly in contact withthe straight portion 12B of the electrode assembly 12 when the sectionof the single battery shown in FIG. 3 is observed with a CT scan usingX-rays. The sentence, “the convex parts 225 support the straight portion12B of the electrode assembly 12” includes a case in which the convexparts 225 are directly or indirectly in contact with the straightportion 12B of the electrode assembly 12 when the sections of thebatteries are observed with the CT scan using X-rays in a state in whichthe plurality of batteries are arranged with the long wall portions 222being opposed and bound by the restraining member (the state in whichthe plurality of batteries are pressed in the direction orthogonal tothe long wall portions 222).

The convex parts 225 of the singe battery may be away from the straightportion 12B of the electrode assembly 12 when the long wall portions 222are not pressed. Such a battery is preferable, because it is relativelyeasy to form the convex parts 225 on the case main assembly 22.

Each of the convex parts 225 extends continuously substantiallythroughout the entire X-axis direction of the long wall portion 222. Inother words, a dimension in the X-axis direction of the convex part 225is substantially the same as a dimension in the X-axis direction of theelectrode assembly 12 housed in the case 20.

The short wall portions 223 connect the end portions of the paired longwall portions 222, 222 arranged parallel to each other at an interval inthe Y-axis direction. In this way, the paired long wall portions 222,222 and the paired short wall portions 223, 223 form the rectangularcylindrical peripheral wall 221.

The lid body 24 is placed on an opening peripheral edge portion of thecase main body 22 to close an opening of the case main body 22. The lidbody 24 has a shape conforming to an outer peripheral edge (outline) ofthe case main body 22 in a plan view. In other words, the lid body 24 isa rectangular plate material long in the X-axis direction and havingfour arc-shaped corners in the plan view.

Moreover, the lid body 24 is provided with paired terminal through holes240, 240, a gas release vent 242, and a filling portion 244 (see FIG.2). The paired terminal through holes 240, 240 are formed at an intervalin the X-axis direction in the lid body 24. The gas release vent 242 hasa thin-walled portion and is formed at a center of the lid body 24. Thethin-walled portion in the embodiment is in a Y shape. The gas releasevent 242 releases gas in the case 20 by tearing the thin-walled portionto connect the inside and the outside of the case 20 when internalpressure (gas pressure) in the case 20 exceeds a predetermined value. Inthis way, the gas release vent 242 reduces the increased internalpressure of the case 20. The filling portion 244 has an electrolytesolution filling hole 245 formed in the lid body 24 and a plug body 246for closing the electrolyte solution filling hole 245. The electrolytesolution filling hole 245 is an opening through which the electrolytesolution is filled into the case 20. The plug body 246 is fitted intothe electrolyte solution filling hole 245 after the filling to therebyclose the electrolyte solution filling hole 245.

The electrode assembly 12 has a band-shaped positive electrode(electrode as a positive electrode) 120, a band-shaped negativeelectrode (electrode as a negative electrode) 122, and band-shapedseparators 124. The positive electrode 120 and the negative electrode122 are wound into an elliptic cylindrical shape with separators 124interposed therebetween and while displaced from each other in a widthdirection (a direction orthogonal to a longitudinal direction of theband-shaped electrodes, i.e., the X-axis direction in FIG. 1) to therebyform the electrode assembly 12 (see FIG. 2). The elliptic cylindricalshaped electrode assembly 12 has an elliptic sectional shape (an outlineof the section) along the Y-Z plane.

In the following description, the end portions in the Z-axis of theelectrode assembly 12 (the elliptic shaped section) which are curvedportions on the peripheral face of the electrode assembly 12 (i.e., theportions where the positive electrode 120 and the negative electrode 122are alternately layered while being curved with the separatorsinterposed therebetween) will be referred to as curved portions 12A. Theportion of the electrode assembly 12 positioned between the curvedportions 12A, which is a substantially straight portion on a peripheralface of the electrode assembly 12 (i.e., the portion where the positiveelectrode 120 and the negative electrode 122 are alternately layered insubstantially straight states with the separators interposedtherebetween), will be referred to as the straight portion 12B. Thediameter in the Z-axis direction of the elliptic shape will be referredto as the major axis and the diameter in the Y-axis direction of theelliptic shape will be referred to as the minor axis.

The positive electrode 120 is formed by a band-shaped sheet of aluminumfilm supporting a positive active material on its surface, for example.The negative electrode 122 is formed by a band-shaped sheet of copperfilm supporting a negative active material on its surface, for example.Each of the positive electrode 120 and the negative electrode 122 has aportion not coated with the active material at an end edge portion inthe width direction (X-axis direction). As a result, at end portions inthe width direction (X-axis direction) of the electrode assembly 12,aluminum film and copper film not coated with the active materials areexposed. In this manner, the electrode assembly 12 has a positive-sideprotruding part (a positive electrode of the electrode assembly) 126formed by only the positive electrode 120 (the portion not coated withthe positive active material) protruding at one end portion in the widthdirection (X-axis direction) of the electrode assembly 12 and anegative-side protruding part (a negative electrode of the electrodeassembly) 126 formed by only the negative electrode 122 (the portion notcoated with the negative active material) protruding at the other endportion in the width direction (X-axis direction).

The electrode assembly 12 formed as described above is housed into abag-shaped insulating member 30 (described later) and then housed intothe case 20 so that one side of a substantially rectangular frame-shapedsection of the case 20 (e.g., a section of the long wall portion 222extending in the substantially vertical direction in FIG. 3) and thestraight portion 12B of the electrode assembly 12 are positioned alongeach other. Specifically, the electrode assembly 12 is housed in thecase 20 in such an attitude that a direction of the winding axiscorresponds to the longitudinal direction (X-axis direction) of the case20 and that the major axis direction corresponds to the direction of thenormal to the bottom wall portion (Z-axis direction).

The insulating member 30 is formed into the bag shape having an openupper portion (upper end in the Z-axis direction) by bending asheet-shaped member cut into a predetermined shape and having aninsulation property. The insulating member 30 is disposed between thecase 20 (specifically, the case main body 22) and the electrode assembly12. In other words, the electrode assembly 12 is put into the insulatingmember 30 and then housed into the case 20. The insulating member 30insulates the case 20 and the electrode assembly 12 from each other. Theinsulating member 30 in the embodiment is made of polypropylene,polyphenylene sulfide, or the like, for example.

The support members 32 are disposed in corner portions of the sectionalong the Y-Z plane of the case 20 (the substantially rectangularframe-shaped section (see FIG. 3)) to support (or press) the curvedportions 12A toward the inside of the electrode assembly (radiallyinwardly). In this manner, because the support members 32 are disposedin the corner portions of the section in the case 20, the supportmembers 32 are supported by the case 20 from two directions (e.g., thelower left support member 32 in FIG. 3 is supported by the bottom wallportion 220 and the long wall portion 222). In this way, the supportmembers 32 can effectively support the curved portions 12A of theelectrode assembly 12 toward inside. The support members 32 are disposedin the respective four corner portions in the case 20. Each of thesupport members 32 in the embodiment is a cylindrical member made ofresin such as polypropylene and has substantially the same length as alength of the electrode assembly 12 in the X-axis direction. The supportmembers 32 are disposed while being elastically deformed (concretely,while being pressed by the curved portions 12A toward inner peripheralfaces of the corner portions of the case 20) between the insulatingmember 30 disposed along an inner peripheral face of the case 20 and thecurved portions 12A of the electrode assembly 12 and support the curvedportions 12A with resilience generated by the elastic deformation.

In the specification, the sentence, “the support members 32 (supportportions) support the curved portions 12A of the electrode assembly 12”includes a case in which the support members 32 are directly orindirectly in contact with the curved portions 12A of the electrodeassembly 12 when the section of the single battery shown in FIG. 3 isobserved with a CT scan using X-rays. The sentence, “the support members32 (support portions) support the curved portions 12A of the electrodeassembly 12” includes a case in which the support members 32 aredirectly or indirectly in contact with the curved portions 12A of theelectrode assembly 12 when the sections of the batteries are observedwith the CT scan using X-rays in a state in which the plurality ofbatteries are arranged with the long wall portions 222 being opposed andbound by the restraining member (the state in which the plurality ofbatteries are pressed in the direction orthogonal to the long wallportions 222 (See FIG. 10)).

It is preferable that the support members 32 are elastically deformeddue to contact between the support members 32 and the curved portions12A. In this way, by utilizing the resilience due to the elasticdeformation of the support members 32, it is possible to support thecurved portions 12A.

The current collectors 14 are disposed along the electrode assembly 12in the case 20 and provide conductivity between the protruding parts 126of the electrode assembly 12 and the terminal portions 16. The battery10 in the embodiment includes the current collector 14 for the positiveelectrode and the current collector for the negative electrode. Thecurrent collector 14 for the positive electrode provides conductivitybetween the protruding part 126 on the positive electrode side and theterminal portion 16 for the positive electrode. The current collector 14for the negative electrode provides conductivity between the protrudingpart 126 on the negative electrode side and the terminal portion 16 forthe negative electrode. In the embodiment, the current collector 14 forthe positive electrode is made of aluminum, an aluminum alloy, or thelike, for example. The current collector 14 for the negative electrodeis made of copper, a copper alloy, or the like, for example.

Each of the current collectors 14 has a terminal-side connection portion140 to be directly or indirectly connected to the terminal portion 16and an electrode assembly-side connection portion 141 to be directly orindirectly connected to the protruding part 126 of the electrodeassembly 12. The current collector 14 is formed into a shape(substantially L shape) bent at a boundary portion between theterminal-side connection portion 140 and the electrode assembly-sideconnection portion 141 to conform to the electrode assembly 12 in afront view by bending a plate-shaped metal material cut into apredetermined shape.

Each of the terminal portions 16 is mounted to the lid assembly 24 whilepassing through the terminal through hole 240 in the lid assembly 24.Specifically, the terminal portion 16 has an external terminal 160, arivet 161, and a conductive portion 162. The external terminal 160extends upward outside the case 20. The rivet 161 passes through theterminal through hole 240 in the lid assembly 24 to fix the currentcollector 14 (the terminal-side connection portion 140) and theconductive portion 162 to the lid assembly 24 while providingconductivity between the current collector 14 and the conductive portion162. The conductive portion 162 connects the external terminal 160 tothe current collector 14 to be able to provide conductivity between theexternal terminal 160 and the current collector 14 via the rivet 161.

In the battery 10 formed as described above, in the case 20, thestraight portion 12B is supported (or pressed) toward inside in thelayered direction of the electrodes (the positive electrode 120 and thenegative electrode 122) by the convex parts 225, and also the curvedportions 12A are supported toward inside in the layered direction of theelectrodes 120 and 122 by the support members 32. Therefore, it ispossible to suitably suppress gathering of displacement of theelectrodes 120 and 122 in the curved portions 12A, the gathering causedby repetition of expansion and contraction of the electrode assembly 12during charge-discharge. In this way, it is possible to prevent formingof partial clearances between the electrodes 120 and 122 layered at thecurved portions 12A of the electrode assembly 12. Each of the protrudingpart 126 on the positive electrode side and the protruding part 126 onthe negative electrode side that are connected to the current collectors14 is not pressed by the convex parts 225, because the protruding parts126 have smaller thicknesses than the straight portion 12B of theelectrode assembly 12 pressed by the convex parts 225.

The battery 10 in the embodiment has the structure for supporting thecurved portions 12A of the electrode assembly 12 by utilizing theresilience generated by the elastic deformation of the support members32. Therefore, even if the electrode assembly 12 expands and contractsdue to the charge-discharge or the like, i.e., the electrode assembly 12changes in size (winding diameter), the support members 32 follow thechange in size and can suitably continue to support the curved portions12A.

Because the lengths in the X-axis direction of the support members 32 inthe embodiment are substantially the same as the length in the X-axisdirection of the electrode assembly 12, substantially the entire curvedportions 12A in the X-axis direction are supported by the supportmembers 32. Therefore, substantially throughout the X-axis direction ofthe curved portions 12A, it is possible to prevent forming of thepartial clearances between the layered electrodes 120 and 122.

An electric storage device and an electric storage apparatus are notlimited to those in the above-described embodiment but can be changed invarious ways without departing from the gist of the invention.

Specific structures of the support portions (support members) 32 are notlimited. Although the support members 32 in the embodiment are separatefrom the insulating member 30, the case 20, and the like, the supportportions may be formed as parts of the insulating member 30, parts ofthe case 20, or the like.

For example, as show in FIG. 4, as support portions 32A, an insulatingmember 30 may be curved to bulge toward curved portions 12A, and curvedportions of the insulating member 30 may support the curved portions 12Ain corner portions in the case 20. Alternatively, as support portions,corner portions of the case 20 may bulge inward similarly to theinsulating member 30 shown in FIG. 4 and parts of the bulging case 20may support the curved portions 12A.

In this structure, the support portions 32A are formed by using theparts of the case 20 or the insulating member 30 and therefore, it ispossible to reduce the number of parts forming the battery 10 ascompared with a case in which the members forming the support portionsare disposed separately.

Although the support members (support portions) 32 in the embodimentsupport the curved portions 12A by using the resilience generated by theelastic deformation, the invention is not limited to it. Supportportions (support members) may be formed by members such as rigid bodieswhich are not elastically deformed or which are hardly elasticallydeformed as in the above case in which the support portions are formedby using the parts of the case 20, for example. Even with such hardsupport portions (support members), it is possible to prevent forming ofthe partial clearances between the layered electrodes 120 and 122 in thecurved portions 12A, if the curved portions 12A are supported toward theinside of the electrode assembly 12.

Although the support members 32 are respectively disposed in the fourcorner portions in the case 20 in the battery 10 in the aboveembodiment, the invention is not limited to it. The support portions(support members) may be disposed only either in the opposite cornerportions on a side of the bottom wall portion 220 or the opposite cornerportions on a side of the lid assembly 24. With this structure, it ispossible to prevent forming of the partial clearances between thelayered electrodes 120 and 122 in the curved portion 12A at least on oneside in the major axis direction (Z-axis direction). In this way, ascompared with the structure in which only the straight portion 12B ofthe electrode assembly 12 is supported toward the inside in the layereddirection of the electrodes 120 and 122, intervals between theelectrodes 120 and 122 forming the electrode assembly 12 become narrow,which increases the charge-discharge efficiency.

Moreover, the number of electrode assemblies 12 housed in the case 20 isnot limited. Although the one electrode assembly 12 is housed in thecase 20 in the above embodiment, two electrode assemblies 12, 12 may behoused in one case 20A, for example, as shown in FIG. 5. Alternatively,three or more electrode assemblies 12, 12, . . . may be housed in onecase. In this case, support members (support portions) 32 are preferablydisposed at positions between the curved portions 12A, 12A in a Y-axisdirection in addition to corner portions as shown in FIG. 5.

Although the insulating member 30 in the above embodiment is formed byfolding the sheet-shaped member having insulation property into the bagshape, i.e., the insulating member 30 in the above embodiment can bereturned into the sheet shape when unfolded, the invention is notlimited to it. The insulating member 30 may be formed into a bag shape(i.e., formed into the bag shape by gluing, welding, or the like).

Although the support members (support portions) 32 in the embodimenthave substantially the same lengths as the length of the electrodeassembly 12 in the X-axis direction, the invention is not limited tothis structure. The support members may have greater lengths than thelength of the electrode assembly 12 in the X-axis direction.

Although the convex parts 225 in the above embodiment continuouslyextend in the X-axis direction, the invention is not limited to it. Theconvex parts may extend intermittently in the Z-axis direction. Althoughthe plurality of convex parts 225, 225, . . . are continuously arrangedin the Z-axis direction on each of the long wall portions 222, theinvention is not limited to this structure. On each of the long wallportions 222, the plurality of convex parts 225, 225, . . . may bearranged at intervals in the Z-axis direction. Sectional shapes of theconvex parts 225 along the Y-axis direction and the Z-axis direction arenot limited to the triangular angle shapes. For example, as shown inFIG. 6, convex parts 225A may be formed to have arc-shaped sections. Asshown in FIG. 7, convex parts 225B may be formed to have portions (tipend portions in a protruding direction) which come in contact with anelectrode assembly 12 and are flat faces along the straight portion 12Bof the electrode assembly 12. Convex parts 225 may be formed bypartially increasing thicknesses of long wall portions 222. Although theinsulating member 30 is not shown in FIG. 6 and FIG. 7, the insulatingmember 30 is disposed between the case 20, and the electrode assembly 12and the support members 32 in the actual battery 10. Although theplurality of convex parts 225, 225, . . . extend to boundaries betweenthe long wall portions 222 and the short wall portions 223 on each ofthe long wall portions 222, the invention is not limited to thisstructure. For example, a plurality of convex parts 225, 225, . . . maybe formed only at positions near a center in an X-axis direction of eachlong wall portion 222.

Although the secondary battery (lithium ion secondary battery) which canbe charged and discharged has been described in the above embodiment,the battery may be of any type and size (capacity). Although thelithium-ion secondary battery has been described as an example of theelectric storage device in the above embodiment, the invention is notlimited to it. For example, the invention can be applied to varioussecondary batteries, a primary battery, and an electric storage deviceof a capacitor such as an electric double layer capacitor.

What is claimed is:
 1. An electric storage device, comprising: anelectrode assembly in which electrodes are wound such that paired curvedportions and a straight portion connecting the paired curved portionsare formed; a case which houses the electrode assembly, the casecomprising a convex part only protruding toward the straight portion ofthe electrode assembly to support the straight portion; a supportportion which is in contact with the curved portion and supports thecurved portion toward an inside of the electrode assembly; and aninsulating member disposed between the case and the electrode assemblyto insulate the case from the electrode assembly, wherein the supportmember is detachably attached to the insulating member, and wherein thesupport member is configured to be elastically deformed due to contactbetween the support member and the curved portion.
 2. The electricstorage device according to claim 1, wherein the support portionsupports at least one of the paired curved portions of the electrodeassembly.
 3. The electric storage device according to claim 1, whereinthe case has a substantially rectangular frame-shaped section and housesthe electrode assembly such that a side of the substantially rectangularframe-shaped section extends along the straight portion, and wherein thesupport portion is disposed in a corner portion of the substantiallyrectangular frame-shaped section in the case.
 4. The electric storagedevice according to claim 1, wherein the support portion is a part ofthe insulating member.
 5. The electric storage device according to claim4, wherein the insulating member includes a portion curved to bulgetoward the electrode assembly, and the curved portion of the insulatingmember supports the curved portion of the electrode assembly.
 6. Theelectric storage device according to claim 1, wherein a dimension of thesupport portion in a direction orthogonal to a winding direction of theelectrodes is substantially equal to or greater than a dimension of theelectrode assembly in the direction orthogonal to the winding direction.7. The electric storage device according to claim 1, wherein the convexpart of the case comprises a plurality of convex parts.
 8. The electricstorage device according to claim 1, wherein the case comprises a wallportion having a wave-shaped inner surface and a wave-shaped outersurface and having a substantially constant thickness, and wherein thewave-shaped inner surface forms a plurality of the convex parts, and theplurality of convex parts support the straight portion of the electrodeassembly at intervals.
 9. The electric storage device according to claim8, wherein the case comprises a substantially rectangular bottom wallportion when viewed in a direction of a normal, wherein the wall portioncomprises paired wall portions extending substantially vertically frompaired long sides of the bottom wall portion, and wherein a maximumclearance between the paired wall portions is greater than a dimensionin a short-side direction of the bottom wall portion.
 10. An electricstorage apparatus comprising the electric storage device according toclaim 1 and a restraining member.
 11. The electric storage deviceaccording to claim 1, wherein the convex part is in contact with thestraight portion.
 12. The electric storage device according to claim 11,wherein the convex part is in contact with the straight portion via theinsulating member disposed between the case and the electrode assembly.13. The electric storage device according to claim 1, wherein theinsulating member abuts the convex part and the straight portion. 14.The electric storage device according to claim 1, wherein the supportportion abuts the curved portion.